Lag screws, also known as lag bolts, are threaded fasteners typically used to mechanically connect together wooden structural members such as posts and beams.
A conventional lag screw has a threaded shank extending from an enlarged head to a pointed free end of the shank. The head is an enlarged hexagonally-shaped head that, when inserted into a socket, forms a non-rotatable connection with the socket that permits torque to be transmitted from the socket to the screw. A typical socket that can be used to install lag screws is disclosed in Garg, U.S. Pat. No. 6,951,156.
It is often required that the head of the lag screw sit flush with or below the wood surface when installed. This requires that a counterbore be drilled in the wood prior to installing the fastener. The counterbore receives the fastener head. The hole of the counterbore must be the correct size to closely receive the head, and the bottom of the counterbore must be at the correct depth so that the head when installed is flush with or the desired distance below the wood surface.
Cutting a counterbore in the wood prior to installing a lead screw adds a step to the fastening process. When installing a large number of lag screws, the added cost can be substantial. Furthermore, if the counterbore is incorrectly located or cut to the wrong depth, the wood member may have to be scrapped or corrective action taken—further increasing cost.
Thus there is a need for an improved method of providing counterbores for receiving the head of lag screws and similar type fasteners. The improved method should enable the fastener to be installed in the same step as providing the counterbore so that the extra step in the fastening process can be eliminated. The improved method should enable the proper depth of cut to be readily determined during the installation of the lag screw, and should be compatible with existing socket wrenches and other conventional fastener drives.